A veteran Navy test pilot and Georgia Tech graduate who joined NASA in 1962, Young was regarded as a savvy engineer in troubleshooting technical problems on his missions and other spaceflights.

Lightfoot said: “I participated in many Space Shuttle Flight Readiness Reviews with John, and will always remember him as the classic ‘hell of an engineer’ from Georgia Tech, who had an uncanny ability to cut to the heart of a technical issue by posing the perfect question -- followed by his iconic phrase, ‘Just asking...’

Young, who joined NASA in 1962, also served as chief of the agency's astronaut corps from 1974 to 1987. He retired in 2004.

"John was more than a good friend," former US President George H.W. Bush said in a statement. "He was a fearless patriot whose courage and commitment to duty helped our nation push back the horizon of discovery at a critical time."

Astronaut Terry Virts tweeted: "Rest In peace John Young. You were one of my heroes as an astronaut and explorer and your passion for space will be missed."